<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>border-radius 画三角形和对话框</title>
    <style>
        .triangle {
            width: 0px;
            height: 0px;
            margin: 50px auto;
            border-top: 50px solid transparent;
            border-right: 0 solid #f00;
            border-bottom: 50px solid transparent;
            border-left: 50px solid #00f;
        }
        .dialog {
            background-color: #6a6;
            margin: 50px auto;
            width: 400px;
            color: #fff;
            height: 30px;
            line-height: 30px;
            padding: 10px;
            border-radius: 6px;
            position: relative;
        }

        .dialog::before {
            content: '';
            border-left: 0 solid #6a6;
            border-right: 10px solid #6a6;
            border-top: 10px solid transparent;
            border-bottom: 10px solid transparent;
            position:absolute;
            left: -10px;
            top:14px;
        }
    </style>
</head>
<body>
    <div class="triangle"></div>
    <div class="dialog">
        Hello Everyone! Hello World!
    </div>
</body>
</html>